The process of this invention was developed in order to produce extremely pure beta silicon carbide powder of submicron size. Such finely divided material may be used in other known silicon carbide article forming processes in order to produce silicon carbide articles of high strength and purity. Such processes include extruding and injection molding of powder with suitable binder materials, as well as slip casting of the powder.
The development of various processes for making silicon carbide in different forms is typified by the prior art patents cited in a novelty study conducted on this subject matter. These patents represent the state of the art as best we know it. The patents cited included the following.
U.S. Pat. No. 966,399 discloses a process for purification of chemically inert electrometallurgical products such as carbides of silicon, boron, etc. The patent does not have any teaching relative to the formation of highly pure beta silicon carbide in a submicron size range.
U.S. Pat. No. 1,134,081 teaches a process by which silicon carbide may be manufactured. The material manufactured, however, is not a finely divided, high purity grade, of beta silicon carbide powder. It is a rather crude process for making various carbides of silicon and represents the state of the art at that time.
U.S. Pat. No. 3,403,008 is directed to a method of making metal carbide fibers of small diameter but of extended length. Example 6 of the patent shows how to make silicon carbide fibers. It shows the immersion of a rayon fiber in silicon tetrachloride liquid, a drying of that fiber so coated, and then a pyrolyzation and carborization of the product in order to produce a silicon carbide fiber. The patent does not teach a method similar to the one set forth in this application for making an extremely finely divided, high purity, beta silicon carbide powder.
U.S. Pat. No. 3,719,452 discloses in Example X thereof, a method for producing an extremely hard body of beta silicon carbide. The silicon carbide produced is not a finely divided, submicron material as is the case when the method of the present invention is followed.
U.S. Pat. No. 3,947,550 discloses a process for making a complex shaped article of silicon carbide in which some alpha silicon carbide particles are bonded together by a beta phase silicon carbide which is formed by pyrolyzing the binder used to hold the initial alpha silicon carbide particles in a particular shape and then siliciding the pyrolyzed binder. The patent does not teach a method for producing submicron size, extremely pure beta silicon carbide powder.